1. Technical Field
The present invention relates to a break pattern which is formed by etching on a line to be cut of a silicon wafer having crystalline properties, a silicon wafer and a silicon substrate.
2. Related Art
As a liquid ejecting head which ejects liquid droplets from a nozzle opening by causing a pressure of liquid in a pressure chamber to change, there are, for example, an ink jet type recording head (hereinafter, simply referred to as a recording head) used for an image recording apparatus such as a printer, a color material ejecting head used for production of a color filter such as for a liquid crystal display, an electrode material ejecting head used for formation of an electrode of an organic EL (electroluminescent) display, a FED (surface-emitting display) or the like, and a bio-organic matter ejecting head used for production of a biochip (biological and chemical element).
When giving as an example a case of the recording head mentioned above, the head is provided with a nozzle forming member that has a plurality of nozzle openings, a passage forming member that forms a liquid passage including a pressure chamber communicating with the nozzle openings, an actuator unit that includes a pressure generating device for generating a pressure change to the liquid in the pressure chamber, and the like. As for these constituent members, particularly the passage forming member, in order to respond to a densification of the recorded image and speedup of the recording operation, an improvement of processing density and processing precision is required. Therefore, as materials for the passage forming member, a base material having a crystalline property such as silicon being able to form a minute shape with good dimensional precision is preferably used.
In a case where the passage forming member is formed using silicon as a base material, for example, a plurality of regions for the passage forming member are formed by dividing a substantially circular silicon wafer, and a portion to be the liquid passage for each region is formed by etching. In addition, a plurality of small through holes is drilled on a line to be cut by the same etching and a break pattern is formed. In this break pattern, a portion between the through holes adjacent to each other becomes weak, and this portion is broken by applying an external force and is divided into multiple portions. Thereby, it is possible to obtain a plurality of passage forming members from one silicon wafer.
According to the above-mentioned break pattern, in the silicon wafer assuming a surface as a (110) face, there is a case that a residual portion which consists of a (111) face slanted with respect to the surface of the silicon wafer is intentionally left at a portion in each through hole (for example, see JP-A-2006-175668). Thereby preventing a malfunction caused when the break pattern is broken carelessly.
However, it is difficult to manage the shape of the residual portion as described above and also its size varies easily due to variation of the etching (variation of etching time). If the size of this residual portion varies, the strength of the fragile portion which is formed between the adjacent through holes varies and there is a possibility that the line to be cut cannot be cut stably. In other words, there is a possibility that, for example, an unintended portion is cleaved, or debris of the residual portion might be scattered. In addition, in order to be more stably cut on the line to be cut, as shown in FIG. 8A, there is a break pattern such that through holes 84 are formed in the shape of a parallelogram by a first (111) face 82 and a second (111) face 83 which are perpendicular to a (110) face which is a surface 81 of the silicon wafer, and acute angle portions of each through hole 84 are opposed to at the adjacent through holes 84. In this case, a space between the acute angle portions of the adjacent through holes becomes a line to be cut. However, the internal side of each acute angle portion is difficult to etch, and a third (111) face inclined with respect to the surface 81 of the silicon wafer is easily left as a residual portion 85 due to etching variations (see FIG. 8B). If these residual portions 85 remain, not only is there a fear of being cut in a line different from the line to be cut (for example, the dashed line in FIG. 8B), but also there is a possibility that the cutting is not performed or debris is scattered.